Re: [PATCH 6/8] mm: Store compound_dtor / compound_order as bytes
From: Michal Hocko <mhocko@kernel.org>
Date: 2017-12-19 08:19:58
On Sat 16-12-17 08:44:23, Matthew Wilcox wrote:
From: Matthew Wilcox <redacted> Neither of these values get even close to 256; compound_dtor is currently at a maximum of 3, and compound_order can't be over 64. No machine has inefficient access to bytes since EV5, and while those are still supported, we don't optimise for them any more.
Hmm, so the improvement is the ifdef-ery removale, right? Beucase this will not shrink the structure size AFAICS. I think that the former is a sufficient justification. Maybe you should spell it out.
Signed-off-by: Matthew Wilcox <redacted>
Acked-by: Michal Hocko <mhocko@suse.com>
quoted hunk ↗ jump to hunk
--- include/linux/mm_types.h | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-)diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 5521c9799c50..1a3ba1f1605d 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h@@ -136,19 +136,8 @@ struct page { unsigned long compound_head; /* If bit zero is set */ /* First tail page only */ -#ifdef CONFIG_64BIT - /* - * On 64 bit system we have enough space in struct page - * to encode compound_dtor and compound_order with - * unsigned int. It can help compiler generate better or - * smaller code on some archtectures. - */ - unsigned int compound_dtor; - unsigned int compound_order; -#else - unsigned short int compound_dtor; - unsigned short int compound_order; -#endif + unsigned char compound_dtor; + unsigned char compound_order; }; #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS-- 2.15.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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